1. Field of the Invention
The present invention relates to an ignition timing controlling apparatus of an internal combustion engine, especially to an ignition timing controlling apparatus which controls ignition timing of the internal combustion engine so as to be at the time when the maximum torque of the internal combustion engine is obtained.
2. Description of Related Art
As the conventional ignition timing controlling apparatus of an internal combustion engine, there are ones which are disclosed in Japanese Patent Application Laid-Open No. 57-59060 and in Japanese Patent Application Laid-Open No. 57-b 59061. FIG. 1 is a longitudinal sectional view showing a construction of major parts of the engine. In the figure, reference numeral 1 is an air cleaner for cleaning air taken into the engine. The air having passed through aforesaid air cleaner 1 passes through an air flow meter 2 for measuring the air intake quantity, a throttle valve 3, and an intake manifold 4 in this order, and is supplied to a cylinder 5 of the engine. The cylinder 5 is surrounded by a water jacket for cooling. At the water jacket, a water temperature sensor 6 for detecting cool water temperature is provided. At the head of the cylinder 5 is an ignition plug 11. At the upper side portion of the engine, there is provided a distributor 8 which synchronizes with the rotation of the engine and distributes high voltage to the ignition plug 11. At the distributor 8, there is provided a crank angle sensor 7 for detecting a rotational angle (crank angle) of the engine.
The crank angle sensor 7 outputs a reference position pulse, for example, at every reference position of the crank angle (every 180.degree. for four-cylinder engine, every 120.degree. for six-cylinder engine) and outputs a unit pulse at every unit angle (for example every 1.degree.). And in an ignition control device 12 to be described later, by calculating the number of unit pulses after the reference pulse is inputted, the crank angle at that time can be obtained. In addition, the number of revolutions of the engine can also be obtained by measuring the frequency or cycle of the unit angle pulse.
An air intake quantity signal S1 outputted from the air flow meter 2 indicating load of the engine, a water temperature signal S2 outputted from the water temperature sensor 6, and a crank angle signal S3 outputted from the crank angle sensor 7 are given to the ignition control device 12. The ignition control device 12 employs a microcomputer comprising, for example, CPU, RAM, ROM, input/output interface and so on. The ignition control device 12 carries out operations corresponding to each of the given signals to calculate the ignition timing, and outputs an ignition signal S7 to an ignition unit 13 so that the ignition plug 11 is ignited at the ignition timing thereof. The outputted ignition signal S7 is distributed by the distributor 8 to ignite the ignition plug 11 of the cylinder to be ignited.
The aforesaid calculation is for obtaining the ignition timing by previously storing basic ignition timing .theta..sub.o corresponding to the number of revolutions N of the engine and air intake quantity Q as a map, reading out the map value corresponding to the number of revolutions N of the engine and the air intake quantity Q at that time, and further by adding or multiplying compensation quantities due to water temperature, etc.
FIG. 2 is a graph explaining the contents of the map for obtaining the basic ignition timing .theta..sub.o, and axes X,Y, and Z respectively show the number of revolutions N, air intake quantity Q, and the basic ignition timing .theta..sub.o. The basic ignition timing .theta..sub.o is predetermined with the number of revolutions N and air intake quantity Q being as parameters so that the pressure building-up rate in the cylinder is the maximum when the output torque of the engine is the maximum.
As the conventional ignition timing controlling apparatus is constructed as above, there is a problem that the ignition timing cannot be controlled so as to be at the time when the maximum torque is obtained, in the case where MBT point (Minimum Advance for Best Torque) at the time of map setting of the ignition timing is different from MBT point at the time of actual usage of the engine due to elapsing change of the engine characteristic and dispersion in manufacturing, etc.